The present invention relates to a safety device and, in particular, to a versatile personnel safety device for reducing the risk of injury to personnel engaged in work in elevated or vulnerable positions, such as high buildings or the deck of a boat or ship.
Personnel safety appliances, such as vertical fall arrest devices, are an important accessory for personnel working in situations where a fall is potentially life-threatening, since they enable the hazard of a fall to be minimised. Vertical fall arrest systems are known which employ a safety line such as a flexible cable for engagement, in a fall arrest situation, by a fall arrest device. Such systems require intermediate support brackets to restrain the cable from buffeting against the fixed structure while under wind loading. These systems therefore present a practical problem of enabling the fall arrest device (and the user) to bypass the support brackets without increasing the fall hazard.
Certain known designs attempt to overcome this bypass problem by using a manually operated bracket lock. This requires the user to open and close the bracket when he traverses it. Other known designs require that the user should lean out from the normal climb/descend posture and pull the cable away from the bracket in order to move the fall arrest device past the bracket position. Both of these methods add significantly to the difficulty of the climb, are more tiring and hence possibly increase the fall hazard.
Some very tall structures, such as telecommunication pylons, masts etc., have a number of separate spans of elongate safety element around the structure. This is due to the fact that ladder placement is often along a number of different climbing axes. Such structures may therefore require the detachment and re-attachment of the safety device at any point during the climb or descent, and the ease with which this can be achieved is an important factor in determining the overall safety of the manoeuvre.
One of the drawbacks of the above-described arrangement, in which the structure includes a number of separate spans of elongate safety element around its periphery, is that personnel must detach themselves from one vertical span and undertake a horizontal traverse, perhaps unsecured, before attaching themselves to the next vertical span.
Another disadvantage of known vertical fall arrest devices is that they tend to be uni-directional with regard to their fall arrest capability. For example, where the fall arrest device relies on a cam locking action for gripping the cable, the device needs to be installed on the cable in the correct orientation for effective operation. If it is installed the wrong way up, the cam cannot grip the cable when the device is descending the cable. Hence, it is ineffective as a fall arrest aid.
To overcome this drawback, the device can be configured to prevent incorrect installation. However, this usually increases its complexity and, inevitably, its weight and cost.
Another drawback of unidirectional cam-locking devices is that they are not ideal for use by personnel working on the apex of a roof, or similar structures where the surface slopes in more than one direction. In such circumstances, a common safety cable may be provided which crosses the roof apex and spans both slopes either side of it. If a workman wishes to ascend one side and descend the other, he must re-orient his fall arrest device at the point where the roof slope changes direction. This is analogous to the situation described above in which intermediate horizontal traverses are executed between different vertical spans of safety cable. The workman is at his most vulnerable at the change-over point and it would be preferable if such circumstances could be avoided.
Above all, it is inconvenient to the workman to have to detach and reattach a safety device every time a change in orientation occurs. Such inconvenience is likely to lead to the situation in which the workman takes risks by declining to re-attach his fall arrest equipment to the safety cable for brief periods, thereby adding to the fall hazard.
Cable-mounted fall arrest devices have been proposed which attempt to address this problem by using double cams. One cam is mounted to activate in a fall arrest situation when the device is travelling along the cable in a first direction, whilst the second cam is mounted in the opposite sense and activates in a fall arrest situation when the device is travelling in the opposite direction.
One drawback of these proposed double cam devices is that they are bulky and hence heavy to wear. Their bulk also means that they can only negotiate larger radius curves on the suspended cable, with the result that their applicability is limited. In addition, they can be inconvenient to handle during installation on the cable because the cams have to be manipulated into a position which allows passage of the cable into the mechanism.
It is therefore an object of the present invention to provide a versatile hands-free personnel safety device for reducing the risk of injury to personnel engaged in work in elevated or vulnerable positions, which is adapted to travel along a continuous span of elongate safety line regardless of the orientation of the safety line. It also an object of the present invention to provide a versatile personnel safety device having bi-directional fall arrest capability. It is a still further object of the present invention to provide a versatile personnel safety device which requires minimal manipulation on the part of the user to negotiate intermediate support brackets and/or changes in orientation of a safety line to which the device is attached in use.
The invention is a personnel safety device adapted to be installed in use on a fixed elongate support element in a manner which allows translational movement of the device along said elongate support element, said device comprising a body member having a bore for receiving said elongate support element, slipper means mounted on said body member said slipper means having a control surface oriented substantially parallel to the longitudinal axis of said bore, and connecting means connected at one end to said slipper means and being adapted at its other end for connection to a personnel safety harness, said slipper means being movable in response to sudden loading of the connecting means between a first position in which the control surface allows free passage of the elongate support element through the bore and a second position in which the control surface grips the elongate support element firmly relative to the body member, in which said slipper means maintains the control surface in its orientation substantially parallel to the longitudinal axis of said bore throughout movement of the slipper means between said first and second positions, and characterised in that the body member is provided with ramp surfaces engageable by the slipper means, said ramp surfaces being adapted to effect movement of the slipper means between its first and second positions.
When the device is subjected to rapid acceleration and/or sudden movements, for example in the event of a fall by a workman connected to the device through a lanyard, this is experienced initially by the connecting means which is connected to the slipper means. The slipper means moves in a direction to follow the sudden applied load, such movement occurring fractionally before the body member is able to move. As a result, the slipper means moves from its first position, in which the control surface allows free passage of the elongate support element through the bore of the body member, to its second position, in which the control surface grips the elongate support element firmly relative to the body member. The device thus locks on to the elongate support element and remains in position until such time as the tensile loading is intentionally removed.
If the workman is incapacitated as a result of the fall, he will remain suspended by his safety harness until he is rescued.
Because the slipper means moves in a manner which maintains the control surface in an orientation substantially parallel to the longitudinal axis of the bore of the body member, the device has bi-directional fall arrest capability.
Preferably, the slipper means is mounted in the bore, with the connecting means protruding through an aperture in the body member. In normal use, the slipper means lies in a neutral position at the base of the ramp means, the control surface allowing free passage of the elongate support element through the bore of the body member. However, in a fall arrest situation, the slipper means moves along the ramp means to an active position in which the control surface grips the elongate support element and holds the device fast relative thereto.
In its neutral condition, the slipper means may be urged into light contact with the elongate support element to assist in smooth passage of the device along the element. For example, compression springs may be used to urge the slipper means radially inwardly towards the centre of the bore. However, it is important to note that, whatever resilient means are used bring about this light contact with the elongate support element, the return force is easily overcome and the resilient means on their own are incapable of locking the device onto the elongate support element in a fall arrest situation.
The safety device is part of a fall arrest system which comprises end anchors and intermediate brackets for supporting the elongate element. The device is able to negotiate the intermediate brackets without user intervention, thereby minimising the risks associated with detachment of the line to transfer between adjacent spans of support element.
Preferably, the body member of the device has a slot extending along its length and radially outwardly from the bore to the exterior of said body member for allowing passage of the device past intermediate brackets for the elongate support element. Most preferably, the longitudinal slot is provided in the body member at a circumferential orientation relative to the slipper means other than 180xc2x0xc2x150xc2x0. This means that, should the fall arrest device ever be deployed in a fall arrest situation, the elongate support element does not become compressed into the longitudinal slot by the control surface of the slipper means.
Alternatively, the body member may be tubular with no longitudinal slot. To enable this variant to traverse intermediate brackets supporting the elongate support element, these brackets are provided with an aperture dimensioned to accommodate the body member of the device and have a slot to allow passage of the connecting means past the support point.